Electromagnetic sound reproducer



- 1.637 119 July 1927' F. A. KOLSTER ET AL ELECTROMAGNETIC SOUND REPRODUCER Filed Jan. 18,- 1927 2 Sheets-Sheet 1 fzzvewiaz's IA-KOZaZP J", 5 A. Boar, BY

ATTORNE 1.637.119 July 1927 F. A. KOLSTER ET AL ELECTROMAGNETIC SOUND REPRODUCER Filed Jan. 18, 1 927 2 Sheets-Sheet 2 jzwwiare I [Yb/$292 fl/ifia/zle, BY 4 M ATTORNEY.

Patented July 26, 1927;

UNITED STATES FREDERICK A. KOLSTER AND SIGURD A. SOLLIE,

OF PALO ALTO, CALIFORNIA, AS-

SIGNORS TO FEDERAL TELEGRAPH COMPANY, OF SAN FRANCISCO, CALH'ORNIA, A

CORPORATION OF CALIFORNIA.

ELECTROMAGNETIC SOUND RiEPRODUCER.

Application filed January 18, 1927. Serial No. 161,894.

This invention relates broadly to electromagnetic sound reproducers and more particularly to an electromagnetic sound reproducer which employs a free edge sound reproducing diaphragm.

One of the objects of the invention is to provide a practical construction of free edge sound reproducing diaphragm where- .in mechanical vibrations may be imparted to the-cone shaped sound reproducing diaphragm where the diaphragm is suspended intermediate the apex and peripheral edge thereof.

Another object of the invention is to providean arrangement of conical shaped sound reproducing diaphragm and electromagnetic driver for impartin vibrations there- I to where the cone shaped diaphragm is supported intermediate its apex and peripheral edge by aflexible membrane which is arranged to center the diaphragm with respect to the electromagnetic "driver while permitting free movement of the diaphragm.

Still another object of our invention is to provide a pneumatic cushioning means for a free edge sound reproducing for eliminating the tendency of blasting of the free edge of the diaphragm.

The invention will be more clearly underdiaphragm HEISSUED' namic type which has been found to be very efl'ective in the reproduction of the entire range of musical notes encountered in radio broadcast reception.

The cone shaped diaphragm is free at its periphery and at the apex thereof but is supported intermediate the apex and peripheral' edge. An armature winding is carried by the cone shaped sound reproducing diaphragm and this winding normally floats within a magnetic gap between the pole faces of the electromagnetic system. The cone is wholly supported intermediate the apex and peripheral edge thereof so that the free edge normally floats without a peripheral support.

Referring to the drawings in detail, reference character 1 designates the electromagnetic driving mechanism enclosed in a housing 2. The electromagnetic driving mech anism is carried by supporting bracket 3 which protrudes from the base member 4. The electromagnetic driving mechanism is of the electrodynamic type in which a magnetic circuit is provided through the shell frame 5, 6 and 7, and through the magnetic pole member'iB which protrudes through the shell closure f forming an annular magnetic gap 9 in which the cylindrical bobbin 10 is ar- I stood by reference to the following specification and theaccompanying drawings, wherein: a

Figure 1 is a side elevation partially in cross-section of the electromagnetic driving mechanism and the conical shaped sound re producing diaphragm "mounting constituting the invention Fig. 2 is a cross-sectional view taken on line 2.-2 of Fig. 1; and Fig.

3 illustrates a theoretical view showing the 40 arrangement of the free edge cone shaped ranged to float. The cylindrical bobbin 10 is secured to the surface of the conical shaped sound reproducing diaphragm 11 intermediate the apex 12 and the periphery 13 of the cone shaped diaphragm. The cylindrical bobbin 10 is flared outwardly as .represented at 14 to conform with the shape of the sound reproducing diaphragm 11. The sound reproducing diaphragm 11 is suspended intermediate the apex 12 and the free peripheral edge 13 by flexible means W in order to diaphragm.

Heretofore in the art it has been proposed to rigidly mount a conical shaped soundreproducing diaphragm of the cone typefrom a spring rim at its periphery and move the diaphragm'bodily from the apex thereof on the principle of a plunger. Such I diaphragms have been of relatively large size and more than nine inches in diameter in unconfined air. The present invention is directed to a relatively small size cone shaped sound reproducing diaphragm in association with a driver of the electrodydevelop sustained" sound Waves- 15 which may extend from the supporting member 16. The supporting member 16 is in the form of a ring over which ring member 17 is arranged to slide for. ipping flexible material such as leather t erebetween. The flexible material 15 may be leather, rubber, linen or other sheet-like material or a plurality of cords which extend beneath the outwardly flared portion 14 of the bobbin 10. The bobbin 10 and material 15 are secured in the form of laminated layers to the surface of the'cone shaped diaphragm 11 thereby suspending the cone shapeddiaphragm for movement with rea similar with terminal posts spect to the electromagnetic driving mech anism from a position intermediate the apex and the free edge of the cone. The flexible membrane or material which is stretched from the frame members 16 and 17 provides one wall of a substantially closed chamber or air pocket against which the diaphragm operates. This air pocket provides means for pneumatically damping the diaphragm for preventing blastingor free vibration of the cone. The only escape for the air is through the ammlar gap 9 so that it will be noted that the air is partially, if not almost wholly confined within the chamber.

The bobbin 10 carries an armature coil 19 thereon inthe magnetic gap 9. Variable currents from the outputcircuit of an audio frequency amplification system are passed through the conductors 20 which connect 21 on the frame of the apparatus as represented at 22. The conductors 20 are normall so'small in size and light in weight that tiey may be glued to the surface of the cone shaped diaphragm 11 without impeding the motion of the diaphragm.

A magnetic field is developed by means of field. coil 24 which is wound upon the magnetic member 8 and supplied with power from any suitable source such as a rectifying system which may operate from the usual alternating current lighting circuit in the home.

In order that the response curve of the reproducer may be relatively flat without undesired sharp resonances, we provide a metallic disc 25 adjacent the electromagnetic system for introducing such eddy current fields as will react with the normal fields of the winding 19 produced at certain frequencies to render the operation of the apparatus more uniform.

We have illustrated the invention as applied to a conical shaped sound reproducing diaphragm, but it 'will be understood that a flat or other shape'of diaphragm may be used e ually well.

We ave described our invention in certain preferred embodiments but we desire it to be understood that modifications may be made and that no limitations upon our invention are intended other than are imposed by the scope of the appended claims.

What we claim asnew and desire to secure by Letters Patent of the United States is as follows:

1. An electromagnetic sound reproducer comprising an electromagnetic driving mechanism including a fieldmagnet and an armature winding arranged tocooperate with said field magnet, a conical shaped sound reproducing diaphragm, a frame member surrounding the apex portion of said conical shaped sound reproducing diaphragm, and an annular flexible membrane extending 'between said frame member and said conical shaped sound reproducing diaphragm in a position intermediate the apex and free peripheral edge thereof for suspending said conical shaped sound reproducing diaphragm.

2. An electromagnetic sound reproducer con'iprising an electromagnetic driving mechanism including a field magnet and an armature winding arranged to cooperate with said field magnet, a conical shaped sound reproducing diaphragm, a frame member surrounding the apex portion of said conical shaped sound reproducing diaphragm, and a flexible sheet of material secured at its edge to said frame member and extending along a portion of the convex side of said conical shaped sound reproducing diaphragm in a position intermediate the apex and free peripheral edge thereof for suspending said conical shaped sound reproducing diaphragm for actuation by said electromagnetic driver.

3. An electromagnetic sound reproducer comprising a frame structure, an electromagnetic driver supported on said frame structure, said driver including a magnetic gap, an armature coil support disposed-in said gap, a winding carried by said armature coil support, a conical sha ed sound reproducing diaphragm arrange to carry said coil support, means for flexibly suspending said conical shaped sound reproducing diaphragm in a position intermediate the apex and free peripheral edge thereof, and an annular metallic plate disposed adjacent said electromagnetic driver for broadening the response curve of said electromagnetic sound reproducer.

4. An electromagnetic sound reproducer comprising an electrodynamic driving apparatus including a field magnet and an armature winding, a sound reproducing diaphragm, said sound reproducing diaphragm carrying said armature winding in spacia relation to said field magnet, and a flexible membrane supporting said diaphragm in a position intermediate the apex and free peripheral edge thereof, said flexible membrane forming a closure for an air chamber directly adjacent the sound reproducing diaphragm.

5. An electromagnetic sound reproducer comprising an electrodynamic driver including an armature winding and a field magnet,

a sound reproducing diaphragm connected a flexible memwith said armature winding, brane for supporting said sound reproducing diaphragm intermediate the apex and free peripheral edge thereof, said flexible membrane being stretched across the front of said field magnet and forming an air chamber against which said sound reproducing diaphragm is arranged to operate.

6. An electromagnetic sound reproduce! comprising a frame structure, an electrodylindrical frame and connected with said namic driving apparatus including a field sound reproducing diaphragm intermediate magnet and an armature winding, a conical the apex and free peripheral edge thereof shaped sound reproducing diaphragm arfor formingan air chamber adjacent said 6 ranged to carry said armature winding, a electrodynamic driving apparatus. 15 cylindrical frame member extending from In testimony where -we afiix our signasaid electrodynamic driving apparatus to a tures.

position intermediate the apex and free piJ- ripheral edge of said diaphragm, and a FREDERICK AL-KOLSTER. flexible membrane stretched across said cy- SIGURD A. SOLLIE. 

